TWiki has been ripped apart by all but two developers moving to Foswiki.

Foswiki is very powerful but it stores pages as text files in a RCS, which has lead (in the case of TWiki) to significant scalability issues in large installations. Foswiki is also not based on Catalyst, and doesn't have a live preview (the user must choose between a WYSIWYG editor and a plain text editor). On the plus side, it has a very large number of plugins, and supports structured data.

WebGUI is easier to install but presents a massive case of not invented here syndrome - it reinvented its own modules to deal with databases, forms, authentication, caching, handling HTTP requests etc. An examination of the source code as of November, 2009-Jun-11 shows: Auth.pm, Cache.pm, Form.pm, Session.pm, SQL.pm etc.. MojoMojo builds on the great power of CPAN.

OSS directory site Ohloh.net provides some interesting visualizations of codebase, activity and contributors for a project. Here is how Foswiki, TWiki, and MojoMojo compare, as of November 2009: